Conductivity of middle distillate fuels with a combination of detergent and cold flow improver

ABSTRACT

The disclosure provides conductivity improving concentrates and methods for improving conductivity and reducing risks associated with static discharge in middle distillate fuel compositions, particularly diesel fuels. The conductivity improvement is provided by the combination of a detergent and a cold flow improver, which are preferably and advantageously pre-blended in an additive concentrate. The disclosure is particularly beneficial for ultra-low sulfur fuel compositions in that it provides a conductivity benefit without adding sulfur into the fuel composition.

FIELD OF THE DISCLOSURE

The disclosure relates to compositions and methods for improving theconductivity of middle distillate fuel compositions, particularly dieselfuels and most particularly low sulfur and ultra-low sulfur dieselfuels.

BACKGROUND OF THE DISCLOSURE

Certain middle distillate fuel compositions, particularly diesel fuels,are capable of generating static electricity, particularly when movingrapidly, such as when the fuel is being dispensed into a tanker or otherbulk container or vessel. While diesel fuels are not very volatile, thetankers used to transport diesel fuels are also used to transportgasoline, kerosene and other more volatile and flammable liquids. Evenafter the more volatile fuel is dispensed from the tanker, the vaporsmay still be present and pose a risk of fire or explosion from a sparkgenerated by the discharge of static electricity from the fuelcomposition.

These risks have become more acute in recent years with the increasedpopularity and use of low sulfur fuels and even more acute in recentmonths with the introduction of ultra-low sulfur diesel fuels. Theprocess used to remove the sulfur from the fuels also decreases theconcentration of other polar compounds in the fuel, which in turnreduces the ability of the fuel to dissipate a static charge.

To mitigate the risks of fire or explosion with low and ultra-low sulfurfuels, it has become desirable to add a conductivity improver to thefuel at or prior to the point of dispensing the fuel into a bulkcontainer. The conductivity improver, as the name suggests, improves theconductivity of the fuel, thus permitting any static charge that mightotherwise build up during high volume transport of the fuel to safelydissipate the static charge without generating a spark. Conductivityimprovers are also known as antistatic agents.

The most common type of conductivity improver or antistatic agent usedin fuels, particularly diesel fuels, has been the Stadis® brand ofantistatic agents sold by Innospec Fuel Specialties, LLC, Newark, Del.However, the Stadis® brand of antistatic agents contains sulfur. Becausesulfur is known to have an adverse effect on the equipment used toremove or reduce emissions from a combustion process, adding the Stadis®antistatic agents to the diesel fuel tends to be counterproductive andshorten the life of the equipment.

Therefore, there is a need for compositions and methods that address thebuild-up and discharge of static electricity in middle distillate fuelcompositions.

SUMMARY OF THE EMBODIMENTS

In an embodiment, the disclosure provides an additive concentrate for amiddle distillate fuel composition comprising an antistatic agent, theantistatic agent comprising, in combination, a detergent and a cold flowimprover.

In an embodiment, the disclosure provides a middle distillate fuelcomposition comprising a conductivity-improving amount of an antistaticagent, the antistatic agent comprising a detergent and a cold flowimprover.

In an embodiment, the disclosure provides a method for improving theconductivity of a middle distillate fuel composition, the methodcomprising the step of adding an antistatic agent to a fuel, wherein theantistatic agent comprises, in combination, a detergent and a cold flowimprover.

In an embodiment, the disclosure provides a method of dispensing amiddle distillate fuel composition, the method comprising the step ofadding an antistatic agent to a fuel in an amount sufficient to providea conductivity of at least 25 pS/m at the time and temperature ofdelivery of said fuel, wherein the antistatic agent comprises, incombination, a detergent and a cold flow improver.

Another embodiment of the present disclosure provides a method ofreducing a risk of explosion from static discharge, comprising the stepsof adding an antistatic agent to a middle distillate fuel composition inan amount sufficient to provide a conductivity of at least 25 pS/m atthe time and temperature of the fuel, wherein the antistatic agentcomprises, in combination, a detergent and a cold flow improver.

Additional objects and advantages of the disclosure will be set forth inpart in the description which follows, and/or can be learned by practiceof the disclosure. The objects and advantages of the disclosure will berealized and attained by means of the elements and combinationsparticularly pointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the disclosure or the appended claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS

By improving the conductivity of the fuel, the fuel is better able todissipate a static charge that might be generated by high volumetransportation of the fuel, such as when the fuel is dispensed into atanker truck or rail car. Because the fuel is better able to dissipate astatic charge, the fuel is less likely to generate a spark, which mayignite volatile fumes that might be present in the area, either from thefuel itself or from previous fuels that may have been transported in thetanker.

The combination of detergent and cold flow improver has been used in thepast in a multi-functional additive concentrate for diesel fuels. Such acombination is particularly useful in additive concentrates used fordiesel fuels in colder climates and/or during the winter months. As thetemperature of diesel fuels is lowered, wax crystals or gels begin todevelop in the fuel. Not only does the development of these crystals andgels make the fuel more difficult to pore, but they also tend toaccumulate and plug filters used to remove particulates and impuritiesfrom the fuel.

Cold flow improvers are of two general types: those that depress thepour point of the diesel fuel (known as pour point depressants) andthose that act to improve the flow of the fuel through a filter in thepresence of the wax crystals and gels (known as operability improvers).These operability improvers do not reduce the formation of the crystalsor gels, but rather alter the way in which they form, thus permittingthe fuel to flow through the filter despite the presence of theseundesired consequences of the lower temperature until such time as thefuel warms up and the crystals and gels dissolve.

To ensure that the fuels flow smoothly through the pipelines, therefineries need to meet certain specifications for pour point in thefuels. However, the refiners do not need to meet specifications foroperability (i.e., filter flow). Thus, while refineries may add pourpoint depressants, they do not always include operability additives. Inaddition, because they have different mechanisms of action, the pourpoint additives incorporated into the fuel at the refinery may not haveany effect on filter flow of the fuel. Accordingly, it is common toincorporate operability-type cold flow improvers into the diesel fuel atthe point of distribution, along with other beneficial additives.

One problem with common antistatic agents, like the Stadis® antistaticagents, is that the conductivity benefit dissipates relatively quicklyonce introduced into a composition containing a basic nitrogencomponent. Such components are typically present in fuels and/oradditive concentrates in the form of detergents, dispersants, cetaneimprovers or other ingredients. Thus, these types of antistatic agentsmust be kept in a separate tank at the depot and added separately to thefuel at or near the time of dispensing the fuel into a tanker, forexample, to ensure that the conductivity benefit from such antistaticagents is in fact obtained. Accordingly, these types of antistaticagent, apart from their inherent additional cost, require additionalcosts and complexity in terms of storage, handling and dispensing.

The present embodiments are based on the surprising discovery byApplicants that the combination of detergent and operability-type coldflow improver can be used to provide a conductivity benefit to a dieselfuel. Applicants have also discovered that the conductivity benefitprovided by such a combination is a sustained benefit, such that thedetergent and cold flow improver can be pre-mixed into an additiveconcentrate and provide a conductivity benefit to the fuel months ofeven years afterward when the additive concentrate is added to the fuel.This conductivity benefit has heretofore gone undiscovered in the priorart.

The present embodiments enable an improvement in conductivity of amiddle distillate fuel composition using only components that provideother functional attributes and are otherwise beneficial to the fuel.This is in contrast to prior art teachings and the conventional wisdomof adding antistatic compounds that provide no other benefit to the fueland are added solely for their antistatic properties. The presentembodiments also provide conductivity benefits without addingsulfur-containing compounds like the Stadis® antistatic agents to anultra-low sulfur fuel, and thus provide that benefit as well.

The present embodiments are particularly suited for middle distillatefuel compositions. Middle distillate fuel compositions include, but arenot limited to, jet fuels, diesel fuels, and kerosene. In oneembodiment, the fuel is a low-sulfur fuel having less than about 500 ppmsulfur, more preferably having less than about 350 ppm sulfur. Inanother embodiment, the fuel is an ultra-low sulfur diesel fuel orultra-low sulfur kerosene. Ultra-low sulfur fuels are generallyconsidered to have no more than about 15 ppm of sulfur, more preferablyno more than 10 ppm of sulfur. The term “diesel fuel” is generallyconsidered to be a generic term encompassing diesel, biodiesel,biodiesel-derived fuel, synthetic diesel and mixtures thereof. Alldisclosures herein of parts per million (“ppm”) are by mass unlessotherwise indicated

The present disclosure encompasses jet fuels, although these areconventionally not regarded as “low-sulfur” or “ultra-low sulfur” fuelssince their sulfur levels can be comparatively quite high. Nevertheless,jet fuels may also benefit from the conductivity improvement of thepresent embodiments regardless of their sulfur content.

The terms “combustion system” and “apparatus” used in the disclosureconnote any apparatus, machine or motor that utilize, in whole or inpart, a combustible fuel to generate power. The terms include, forexample, diesel-electric hybrid vehicle, a gasoline-electric hybridvehicle, a two-stroke engine, any and all burners or combustion units,including for example, stationary burners, waste incinerators, dieselfuel burners, diesel fuel engines, automotive diesel engines, gasolinefuel burners, gasoline fuel engines, power plant generators, and thelike. The hydrocarbonaceous fuel combustion systems that may benefitfrom the present disclosure include all combustion units, systems,devices, and/or engines that burn fuels. The term “combustion system”also encompasses internal and external combustion devices, machines,engines, turbine engines, jet engines, boilers, incinerators,evaporative burners, plasma burner systems, plasma arc, stationaryburners, and the like which can combust or in which can be combusted ahydrocarbonaceous fuel.

The middle distillate fuel compositions contemplated by the presentdisclosure can contain other additives. Such additives may be addeddirectly to the fuel or may comprise an additive concentrate which is,in turn, added to the fuel. Examples of conventional fuel additiveswhich may be used include antioxidants, fuel stabilizers, dispersants,antihaze agents, antifoams, cetane number improvers, ignition andcombustion improvers, corrosion inhibitors, biocides, dyes, smokereducers, catalyst life enhancers and demulsifiers, lubricity agents andother standard or useful fuel additives.

Examples of common additives for middle distillate fuel compositionsinclude non polar organic solvents such as aromatic and aliphatichydrocarbons, including toluene, xylene and white spirit, e.g. thosesold under the Trade Mark “SHELLSOL” by the Royal Dutch/Shell Group, orthose sold as AROMATIC 100 and AROMATIC 150 sold by ExxonMobil; polarorganic solvents, in particular, alcohols generally aliphatic alcoholse.g. 2 ethylhexanol, decanol and isotridecanol, dehazers, e.g.alkoxylated phenol formaldehyde polymers such as those commerciallyavailable as NALCO™ 7D07 (ex Nalco), and TOLAD™ 2683 (ex Petrolite),anti-foaming agents e.g. the polyether-modified polysiloxanescommercially available as TEGOPREN™ 5851 (ex Th. Goldschmidt) Q 25907(ex Dow Corning) or RHODORSIL™ (ex Rhone Poulenc); ignition improverssuch as aliphatic nitrates e.g. 2-ethylhexyl nitrate and cyclohexylnitrate; anti-rust agents such as polyhydric alcohol esters of succinicacid derivatives (e.g. commercially sold by Rhein Chemie, Mannheim,Germany as RC 4801™, or by Afton Chemical as HiTEC® 536; anti-oxidantse.g. phenolics such as 2,6-di-tert-butylphenol, or phenylenediaminessuch as N,N′-di-sec-butyl-p-phenylenediamine; metal deactivators such assalicylic acid derivatives, e.g. N,N′-disalicylidene-1,2-propane diamineand; lubricity agents such as fatty acids and esters, (e.g. thosecommercially available as EC831, P631, P633 or P639 (ex Infinium) orHITEC® 580 (ex Afton Chemical), Lubrizols™ 539A (ex Lubrizol), VECTRON™6010 (ex Shell Additives), OLI9000 (ex Associated Octel).

Some of these additives are more commonly added directly at the refinerywhile the others form part of a diesel fuel additive, typically added atthe point of loading into the tanker.

Particularly preferred lubricity additives are derived by the reaction,combination, mixture, or admixture of a hydrocarbyl-substituted succinicanhydride and a hydroxyamine. These additives enhance the lubricatingproperties of the fuel without degrading other performance features ofthe fuel, such as detergency, ignition quality, stability, and so on. Inaddition, non-acidic lubricity additives posing less risk of corrosionto parts contacted by middle distillate fuel compositions and ofreaction with basic components of fuel additive formulations

In one aspect, the term “hydrocarbyl” group is an alkenyl or alkylgroup. The term “hydroxyamine” has general meaning encompassing eithermonohydroxyamine or polyhydroxyamine, such as dihydroxyamine, ormixtures thereof. Examples of useful hydrocarbyl succinic anhydridecompounds include tridecylsuccinic anhydride, pentadecylsuccinicanhydride, tetradecenylsuccinic anhydride, hexadecenylsuccinicanhydride, dodecylsuccinic anhydride, tetradecylsuccinic anhydride,hexadecylsuccinic anhydride, octadecenylsuccinic anhydride,tetrapropylene-substituted succinic anhydride, docosenylsuccinicanhydride, and mixtures thereof.

Examples of hydroxyamines include ethanolamine, diethanolamine,N-alkylethanolamines, N-alkenylethanolamines, N-alkylisopropanolamines,N-alkenylisopropanolamines, isopropanolamine, diisopropanolamine,tris(hydroxymethyl)aminomethane, 3-amino-1,2-propanediol,2-amino-1,3-propanediol, and mixtures thereof, where the alkyl andalkenyl groups, when present, contain 1 to 12 carbon atoms. Other usefulhydroxyamines include 3-amino-1-propanol, 4-amino-1-butanol,5-amino-1-pentanol, 6-amino-1-hexanol, 4-aminophenol, their isomers, andmixtures thereof. Still another group of hydroxyamines have the hydroxylgroup directly bonded to the nitrogen, such as hydroxylamine, andN-alkylhydroxyamines or N-alkenylhydroxyamines where the alkyl oralkenyl group may contain up to 12 carbon atoms.

Also useful are HSA-hydroxyamine compounds in which the free hydroxylgroup has been allowed to react with epoxides such as ethylene oxide,propylene oxide, butylene oxide, glycidol, and the like. The molar ratioof hydrocarbyl-substituted succinic anhydride acylating agent tohydroxyamine can be from about 1:4 to about 4:1, and more preferably isfrom about 1:2 to about 2:1.

Typically, the concentration of the lubricity enhancing additive used ina middle distillate fuel composition falls in the range 10 to 1000 ppm,preferably 10 to 500 ppm, and more preferably from 25 to 250 ppm. Whenmixtures of additives are used the overall additive concentration fallswithin the typical range noted.

For the sake of convenience, the additives may be provided as aconcentrate for dilution with fuel. Such a concentrate typicallycomprises from 99 to 1% by weight additive and from 1 to 99% by weightof solvent or diluent for the additive which solvent or diluent ismiscible and/or capable of dissolving in the fuel in which theconcentrate is to be used. The solvent or diluent may, of course, be thelow sulfur fuel itself. However, examples of other solvents or diluentsinclude white spirit, kerosene, alcohols (e.g., 2-ethyl hexanol,isopropanol and isodecanol), high boiling point aromatic solvents (e.g.,toluene, xylene) and cetane improvers (e.g., 2-ethyl hexylnitrate). Ofcourse, these may be used alone or as mixtures.

The compositions and methods of the present embodiments are capable ofproviding conductivity to a fuel of at least 25 pS/m at the time andtemperature of delivery. This conductivity is sufficient to meet theproposed new ASTM standard for conductivity in diesel fuels (ASTM D975and amendments and appendices thereto) measured according to anyappropriate test procedure, including but not limited to ASTM D2624. Theconductivity benefit is obtained by adding to a middle distillate fuelcomposition the combination of a detergent and an operability-type coldflow improver.

The term “sulfur-containing compounds” used herein connotesorgano-sulfur compounds; including sulfone, polysulfone, linear andbranched aliphatic or aromatic sulfonates, sulfates, sulfides,sulfurized alkenes, polyalkenes, sulfurized polyphenols, sulfonic acids,and salts thereof.

The term “substantially free” when used to in connection with areference to “sulfur” indicates that the relevant compounds contributeno more than 15 ppm of sulfur to the composition when measured accordingto for example, ASTM D2622 or ASTM D4951, preferably no more than 10 ppmof sulfur and most preferably no more than about 5 ppm of sulfur.

Suitable ashless detergents/dispersants include amides, amines,polyetheramines, Mannich bases, succinimides (which are preferred).Metal-containing detergents are also effective. Mixtures andcombinations of detergents may also be used, if desired.

These detergents/dispersants are well known in the patent literature,mainly as additives for use in lubricant compositions, but their use inhydrocarbon fuels has also been described. Ashless dispersants leavelittle or no metal-containing residue on combustion. They generallycontain only carbon, hydrogen, oxygen and in most cases nitrogen, butsometimes contain in addition other non-metallic elements such asphosphorus, sulphur or boron. A particularly useful ashlessdispersant/detergent herein is derived from “high reactive”polyisobutylene (HR-PIB) substituted on a maleic anhydride reacted witha polyamine to achieve a level of about 5.4% nitrogen to achieveenhanced dispersancy. Such a material is available from Afton ChemicalCorporation as HiTEC® 9651; HiTEC® 4247 or HiTEC® 4249. Thedetergent/dispersant can be used in the fuel additive concentrates atlevels of from about 5 to about 50% by weight, more preferably 10-30%.

In one preferred embodiment, the detergent is a succinimide, which hasan average of at least 3 nitrogen atoms per molecule. The succinimide ispreferably aliphatic and may be saturated or unsaturated, especiallyethylenically unsaturated, e.g. an alkyl or alkenyl succinimide.Typically the detergent is formed from an alkyl or alkenyl succinicacylating agent, generally having at least 35 carbon atoms in the alkylor alkenyl group, and an alkylene polyamine mixture having an average ofat least 3 nitrogen atoms per molecule. In another embodiment thepolyamine has 4 to 6 nitrogen atoms per molecule. Preferably it can beformed from a polyisobutenyl succinic acylating agent derived frompolyisobutene having a number average molecular weight of 500 to 10,000and an ethylene polyamine which can include cyclic and acyclic parts,having an average composition from triethylene tetramine topentaethylene hexamine. Thus the chain will typically have a molecularweight from 500 to 2500, especially 750 to 1500 with those havingmolecular weights around 900 and 1300 being particularly useful althougha succinimide with an aliphatic chain with a molecular weight of about2100 is also useful. Further details can be found in U.S. Pat. Nos.5,932,525 and 6048373 and EP-A•432,941, 460309 and 1,237,373.

Examples of suitable metal-containing detergents useful herein include,but are not limited to, such substances as lithium phenates, sodiumphenates, potassium phenates, calcium phenates, magnesium phenates,sulphurised lithium phenates, sulphurised sodium phenates, sulphurisedpotassium phenates, sulphurised calcium phenates, and sulphurisedmagnesium phenates wherein each aromatic group has one or more aliphaticgroups to impart hydrocarbon solubility; the basic salts of any of theforegoing phenols or sulphurised phenols (often referred to as“overbased” phenates or “overbased sulphurised phenates”); lithiumsulfonates, sodium sulfonates, potassium sulfonates, calcium sulfonates,and magnesium sulfonates wherein each sulphonic acid moiety is attachedto an aromatic nucleus which in turn usually contains one or morealiphatic substituents to impart hydrocarbon solubility; the basic saltsof any of the foregoing sulfonates (often referred to as “overbasedsulfonates”; lithium salicylates, sodium salicylates, potassiumsalicylates, calcium salicylates, and magnesium salicylates wherein thearomatic moiety is usually substituted by one or more aliphaticsubstituents to impart hydrocarbon solubility; the basic salts of any ofthe foregoing salicylates (often referred to as “overbasedsalicylates”); the lithium, sodium, potassium, calcium and magnesiumsalts of hydrolysed phosphosulphurised olefins having 10 to 2000 carbonatoms or of hydrolysed phosphosulphurised alcohols and/oraliphatic-substituted phenolic compounds having 10 to 2000 carbon atoms;lithium, sodium, potassium, calcium and magnesium salts of aliphaticcarboxylic acids and aliphatic-substituted cycloaliphatic carboxylicacids; the basic salts of the foregoing carboxylic acids (often referredto as “overbased carboxylates” and many other similar alkali andalkaline earth metal salts of oil-soluble organic acids. Mixtures ofsalts of two or more different alkali and/or alkaline earth metals canbe used. Likewise, salts of mixtures of two or more different acids ortwo or more different types of acids (e.g., one or more calcium phenateswith one or more calcium sulfonates) can also be used. While rubidium,cesium and strontium salts are feasible, their expense renders themimpractical for most uses.

Particularly preferred cold flow improvers for the present embodimentsinclude the operability-type of cold flow improver mentioned previously.This type of cold flow improver improves the ability of the fuel to flowthrough a filter, as determined according to the Cold Filter PluggingPoint Test (ASTM D6371) or the Low Temperature Flow Test (ASTM D4539).Particularly preferred cold flow improvers include acrylates,methacrylates, ethylene vinyl acetate copolymers, chlorinatedhydrocarbons and polyolefins, and alkyl phenols. A most preferred coldflow improver is Altra™ 205 available from Allegheny Petroleum ProductsCorporation. Combinations of cold flow improvers may also be used toadvantage. The cold flow improver is generally present in an amount offrom about 25 to about 100 ppm.

EXAMPLES

The following examples illustrate but do not limit the presentembodiments.

The following components were used in the Examples:

HiTEC® 4130S is a multi-functional fuel additive concentrate availablefrom Afton Chemical. It comprises a succinimide detergent, an esterbased lubricity additive, a corrosion inhibitor, a demulsifier, aromaticsolvents and alcohol cosolvent.

HiTEC® 4130W is a multi-functional fuel additive concentrate availablefrom Afton Chemical having the same essential ingredients as HiTEC®4130S, except that it also includes HiTEC® 4566 cold flow improver fromAfton Chemical.

HiTEC® 4130E is a multi-functional fuel additive concentrate that was apredecessor to HiTEC® 4130W from Afton Chemical. It had the samedetergent and cold flow improver as HiTEC® 4130W, but differed in someof the other ingredients. The samples using HiTEC® 4130E are at least 18months old at the time of testing.

In each example, the additive concentrate was added to an ultralowdiesel fuel available from ExxonMobil at a concentration specified inTable 1. The units “ptb” indicate a concentration in pounds per thousandbarrels.

Conductivity in the samples was determined at room temperature and afterstoring the sample in a freezer until the temperature of the samplereached approximately −20° C. Results are reported in Table 1.

TABLE 1 Conductivity (pS/m) Additive Added Room Concentrate (ptb)HiTEC ® 4566 Temp −20° C. Control 1 None 15 ptb 5 Control 2 None 15 ptb9 Control 3 None 15 ptb 6 Control 4 HiTEC ® 4130S (259) None 23 Example1 HiTEC ® 4130S (259) 15 ptb 154 Example 2 HiTEC ® 4130W (259) None 18552 Example 3 HiTEC ® 4130W (259) None 189 45 Example 4 HiTEC ® 4130W(259) None 190 49 Example 5 HiTEC ® 4130W (259) None 192 32 Example 6HiTEC ® 4130E (262) None 149 Example 7 HiTEC ® 4130E (262) None 143Example 8 HiTEC ® 4130E (262) None 101

These data demonstrate that a conductivity benefit can be obtained in alow sulfur diesel fuel by the combination of a detergent and a cold flowimprover, without the addition of any specialized antistatic agents.Controls 1-3 demonstrate that the addition of the cold flow improveralone to the fuel does not improve conductivity. Control 4 demonstratesthat the detergent alone (in the form of an additive concentrate) alsodoes not improve the conductivity of the fuel. Example 1-5, however,show that a conductivity improvement is seen when the detergent and coldflow improver are combined in a diesel fuel, regardless of whether theyare added separately or as part of a pre-blended additive concentrate.In addition, as noted above, Applicants have discovered that thisbenefit is observed even if the detergent and cold flow improver havebeen mixed together for extended periods of time as in Examples 6-8.

Unlike the special antistatic agents like the Stadis® compounds, thepresent embodiments permit a conductivity benefit to be obtained using asingle additive concentrate if desired, without requiring additionalstorage of handling procedures for the antistatic agents. In addition,the conductivity improvement is obtained without increasing the sulfurcontent of the additive concentrate or the fuel composition.

While particular embodiments have been described, alternatives,modifications, variations, improvements, and substantial equivalentsthat are or can be presently unforeseen can arise to applicants orothers skilled in the art. Accordingly, the appended claims as filed andas they can be amended are intended to embrace all such alternatives,modifications variations, improvements, and substantial equivalents.

1. An additive concentrate for a middle distillate fuel compositioncomprising an antistatic agent, said antistatic agent comprising, incombination, detergent and a cold flow improver.
 2. The additiveconcentrate of claim 1, wherein said additive concentrate issubstantially free of sulfur compounds.
 3. The additive concentrate ofclaim 1, wherein said additive concentrate is substantially free ofsulfur-containing antistatic agents.
 4. The additive concentrate ofclaim 1, wherein said additive concentrate contains no more than 15 ppmof sulfur.
 5. The additive concentrate of claim 1, wherein said fuelcomprises a diesel fuel.
 6. The additive of claim 1, wherein saiddetergent comprises a succinimide.
 7. The additive concentrate of claim1, wherein the cold flow improver comprises a alkyl phenol.
 8. Use ofthe additive concentrate of claim 1 to provide a conductivity measure ofat least 25 pS/m in a middle distillate fuel composition at the time andtemperature of delivery of said fuel.
 9. A middle distillate fuelcomposition comprising an antistatic agent, said antistatic agentcomprising, in combination, a detergent and a cold flow improver. 10.The fuel composition of claim 9, wherein said fuel comprises a dieselfuel.
 11. The fuel composition of claim 10, wherein said fuel containsno more than 15 ppm of sulfur.
 12. The fuel composition of claim 11,wherein said diesel fuel is substantially free of sulfur-containingantistatic agents.
 13. The fuel composition of claim 9, wherein saidmiddle distillate fuel composition is substantially free ofsulfur-containing conductivity improvers.
 14. The fuel composition ofclaim 9, wherein said fuel has a conductivity of at least 25 pS/m at thetime and temperature of delivery of said fuel.
 15. The fuel compositionof claim 9, wherein said detergent comprises a succinimide.
 16. The fuelcomposition of claim 9, wherein said cold flow improver comprises aalkyl phenol.
 17. Use of the fuel of claim 1 in a combustion apparatus.18. A method for improving the conductivity of a middle distillate fuelcomposition comprising the step of adding an antistatic agent to saidfuel in an amount sufficient to provide a conductivity of at least 25pS/m at the time and temperature of delivery of said fuel, wherein saidantistatic agent comprises, in combination, a detergent and a cold flowimprover.
 19. The method of claim 18, wherein said fuel compositioncomprises a diesel fuel.
 20. The method of claim 19, wherein said dieselfuel is substantially free of sulfur-containing antistatic agents. 21.The method of claim 19, wherein said diesel fuel, after addition of saidantistatic agent, contains no more than 15 ppm of sulfur.
 22. The methodof claim 18, wherein said detergent and said cold flow improver are partof a multifunctional additive concentrate.
 23. A method of dispensing amiddle distillate fuel composition comprising the steps of adding to amiddle distillate fuel composition an antistatic agent in an amountsufficient to provide a conductivity of at least 25 pS/m at the time andtemperature of delivery of said fuel, wherein said antistatic agentcomprises, in combination, a detergent and a cold flow improver.
 24. Themethod of claim 23, further comprising the step of dispensing said fuelprior to the conductivity dropping below 25 pS/m.
 25. The method ofclaim 24, wherein said dispensing step comprises dispensing said middledistillate fuel composition into a bulk container.
 26. The method ofclaim 23, wherein said detergent and said cold flow improver arepre-blended in an additive concentrate prior to addition to said fuel.27. The method of claim 23, wherein said middle distillate fuelcomposition comprises a diesel fuel.
 28. The method of claim 23, whereinsaid diesel fuel, after the addition of said antistatic agent, containsno more than 15 ppm of sulfur.
 29. A method of reducing a risk ofexplosion from static discharge, comprising the steps of adding anantistatic agent to a middle distillate fuel composition in an amountsufficient to provide a conductivity of at least 25 pS/m at the time andtemperature of delivery of said fuel, wherein said antistatic agentcomprises, in combination, a detergent and a cold flow improver.
 30. Themethod of claim 29, further comprising the step of dispensing said fuelprior to said conductivity dropping below 25 pS/m.
 31. The method ofclaim 30, wherein said dispensing step comprises dispensing said middledistillate fuel composition into a bulk container.
 32. The method ofclaim 29, wherein said detergent and said cold flow improver arepre-blended in an additive concentrate prior to addition to said fuel.33. The method of claim 29, wherein said fuel composition comprises adiesel fuel.
 34. The method of claim 33, wherein said diesel fuel issubstantially free of sulfur-containing antistatic agents.
 35. Themethod of claim 33, wherein said diesel fuel, after addition of theantistatic agent, contains no more than 15 ppm of sulfur.